Efficient design

Question

What is meant by ‘efficient design’? Explain.

Answer 1

Increased efficiency can be considered in terms of direct reductions in foundation costs, related to the amount of resources/materials used, and also in terms of reductions in indirect costs, eg by preventing foundation failures requiring remedial works, or by reducing waste generated by excavations. The reduction of carbon emissions and embodied energy can also be considered as a measure of increasing ‘efficiency’.

In terms of instances where ‘efficiency’ of design could have been improved, three broad situations can be considered:

A: where foundations have not met the design requirements, typically resulting in the need for remedial works.

B: where the type of foundation selected does not provide the best solution.

C: where foundations have performed adequately, but have been ‘overdesigned’.

These situations can be developed further as follows:

Case A: Where foundation ‘failure’ occurs it is often related to sites where there has been a fundamental misunderstanding of the ground conditions and hence the manner in which the foundations will interact with them, for example where features or conditions on site have not been recognised (eg loose made ground in areas of backfilled ponds or swelling of clays following tree removal). A suitable site investigation including desk study and subsequent ground investigation is essential to identify and quantify hazardous ground conditions, to allow mitigation against the risks that these hazards pose, and inform the design.

Foundation failure could also relate to cases where the performance requirements of the building have not been considered and designed for, for example, where foundation movements are in excess of acceptable building movements.

Case B: Where a foundation type other than that which has been selected could have provided overall benefits and savings, for example where deep trench fill foundations have been used where other solutions such as rafts, piles or ground improvement may have been better solutions.

Case C: Where the ground may be well understood in terms of the stratigraphy, there may be a shortfall of information to allow ‘efficient’ design of the foundations. This could for example relate to inadequate strength data for the ground, with the foundation design becoming less efficient since the design assumptions made are more conservative than actually needed.